This invention relates to improved methods and apparatus for generating electrical energy, heat, and an aluminum hydroxide reaction product from the oxidation of aluminum, especially aluminum waste and other inexpensive aluminum products.
These copending applications deal with various improvements in methods and apparatus for deriving electrical energy from the electrochemical oxidation of various forms of aluminum and its alloys. Although the intended use of the derived electrical energy has been primarily for the propulsion of electric vehicles, some stationary systems may also benefit from the availability of power sources utilizing aluminum, especially aluminum refuse or other inexpensive forms of aluminum, as the primary electrochemical fuel.
To generate electrical energy, the aluminum is consumed in a reaction chamber, wherein it reacts either directly as a consumable anode or indirectly by first yielding an intermediary compound, such as hydrogen, which in turn serves as the anode reactant in a separate electrochemical cell, as described in one embodiment of my afore-cited copending application Ser. No. 20,967, filed Mar. 16, 1979.
Some aluminum alloys containing appreciable concentrations of iron and other impurities tend to corrode at an excessive rate, especially at temperatures above 50.degree. C., and may therefore not be suitable for direct use as consumable anodes in electrochemical cells designed for motor vehicle propulsion. Their indirect use via generation of hydrogen for electrochemical consumption in hydrogen/air fuel cells, as disclosed in my last-mentioned application, may be beneficial for only a limited number of stationary systems. The main reason for the limited applicability of such indirect energy generation from the consumption of aluminum is the relatively high cost of hydrogen/air fuel cells and their relatively low cell voltage and power density.
It is an object of my present invention to provide power sources capable of utilizing a wide variety of inexpensive aluminum alloys, especially those currently lost in refuse, as electrochemical fuel for such widespread applications as the propulsion of electric vehicles.
It is a further object of my invention to provide power sources wherein indirect electrical energy generation from the consumption of aluminum yields higher cell voltages and power densities than those obtainable with hydrogen/air fuel cells.
It is yet another object of my invention to render such power sources far less expensive than those utilizing hydrogen/air fuel cells.
It is still another object of my invention to provide apparatus and methods whereby hydrogen derived from the consumption of aluminum waste or other inexpensive forms of aluminum may serve as a consumable anode reactant in hydrogen/nickel dioxide, hydrogen/silver oxide, hydrogen/hydrogen peroxide and other electrically or chemically rechargeable electrochemical cells.
In my last-mentioned copending application Ser. No. 20,967, filed Mar. 16, 1979, I have also disclosed the use of corrosion-inhibiting additives in the electrolyte from the group comprising stannate ions, gallate ions, indic hydroxide, thallous hydroxide, and mercuric oxide. Each ion or compound of the latter group comprises a species more noble than aluminum, i.e., which plates out spontaneously onto an aluminum surface at the expense of aluminum ions. A piece of aluminum immersed in such an electrolyte would therefore get rapidly covered with an alloy layer rich in the additive metal, and any further dissolution of aluminum would thereafter proceed through the intermediary of this alloy layer, which is much less prone to corrode than the original metal. Electrochemical consumption of aluminum under these conditions might therefore be also viewed as proceeding indirectly via said intermediary alloy layer.
Similarly, zinc compounds, especially zincate ions, are known to react spontaneously with aluminum metal to form metallic zinc and aluminum ions. However, I have found that zinc layers formed on aluminum surfaces in alkaline solutions usually tend to flake off. When a slurry of zinc or zinc-coated particles impinges on an aluminum surface, there is a competition between the rate of further deposition of zinc on the preexisting zinc surfaces and the rate of formation of zinc on the aluminum, with the former usually prevailing. Moreover, the zinc deposited on the aluminum flakes off and breaks up easily, and eventually gets mixed in with the slurry.
The use of aluminum, especially in powdered form, to regenerate zinc from zincate ions in zinc/oxygen or zinc/air batteries has been disclosed by Doniat et al., U.S. Pat. No. 3,981,747, issued Sept. 21, 1976, and by Michelin & Cie, British Pat. No. 1,536,840, published Dec. 20, 1978. However, these patents do not disclose the means for selectively removing the aluminum hydroxide reaction product which is bound to form and accumulate upon prolonged consumption of aluminum in a continuously operating system. Moreover, the use of aluminum in form of a powder is bound to result in appreciable corrosion losses.
It is therefore one of the purposes of my invention to provide the means for continuously recharging a zinc-air battery with aluminum waste and other inexpensive aluminum products so as to generate heat, electrical energy, and aluminum hydroxide, and for selectively separating the aluminum hydroxide from the electrolyte and from the zinc slurry particles.
It is still a further object of my invention to improve the current efficiency and energy conversion efficiency achievable through such an indirect electrochemical consumption of aluminum products.